Chemical & Biomolecular Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2219
Formerly known as the Department of Chemical Engineering.
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Item DIRECT NON-OXIDATIVE METHANE CONVERSION VIA H2-PERMEABLE TUBULAR CERAMIC MEMBRANE REACTOR(2019) Sakbodin, Mann; Liu, Dongxia; Wachsman, Eric D.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Conversion of methane to higher hydrocarbons has the potential as the substitute for liquid petroleum in petrochemical and other chemical industries. Direct non-oxidative methane conversion (DNMC) reaction has attracted much attention given its unique capability to convert methane into C2 (acetylene, ethylene, and ethane), aromatics, and hydrogen, while circumventing the intermediate energy intensive steps found in the conventional indirect “syngas” routes. In addition, DNMC has better atom efficiency compared to the indirect routes since COx products can be avoided. However, the main drawbacks of the DNMC reaction are due to the low methane equilibrium conversion, high endothermicity, and high rate of carbon formation. This dissertation aims to development a novel catalyst/membrane system to circumvent the limitations of the DNMC reaction for the efficient and effective hydrocarbons production. The single iron sites confined in the lattice of silica matrix (Fe/SiO2) is an emerging methane activation catalyst for the DNMC reaction. By coupling the Fe/SiO2 catalyst with the H2-permeable tubular ceramic membrane reactor, part of the hydrogen produced from the DNMC reaction can be removed from the effluent gas, which shifts the equilibrium of the reaction to the product side, and in turn, increases the methane conversion. In addition, different sweep gases (H2, air, O2) can be used to promote different additional capabilities of the membrane reactors. The product distribution of the DMNC reaction can be tuned by either removing or adding H2 to the DNMC reaction. Dual production of higher hydrocarbons and CO (or syngas) from two major global greenhouse gases can be achieved when CO2 is used as the sweep gas. On one side of the membrane tube, CH4 upgrading to C2+ hydrocarbons was realized via DNMC reaction over the Fe/SiO2 catalyst, with co-production of H2 gas. On the opposite side, the hydrogen permeate reacted with CO2 sweep to form CO and H2O via the RWGS reaction. Autothermal operation of the membrane reactor is potentially feasible by providing the heat required for the endothermic DNMC reaction from the heat released from the combustion of permeated H2 when O2 is used as sweep gas. In addition, a dual DNMC reactor and H2-permeable membrane system was proposed in order to enhance the production of aromatics from CH4, with pure H2 as a beneficial byproduct. By recycling the effluent gas to the DMNC reactor after partial H2 removal, in certain conditions, the aromatics yield reached >50%, which is significantly higher than single-pass results.Item REVISITING THE ELECTROCHEMICAL STABILITY WINDOW OF SOLID ELECTROLYTES FOR THE DEVELOPMENT OF BULK-TYPE ALL-SOLID-STATE LITHIUM BATTERIES(2018) Han, Fudong; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bulk-type all-solid-state lithium-ion batteries (ASSLIBs) are being considered as the ultimate solution for safe lithium-ion batteries due to the replacement of volatile and flammable liquid electrolytes by nonflammable inorganic solid electrolytes (SEs). Significant advances have been made in achieving superionic SEs with a wide electrochemical stability window (ESW) from 0 to 5 V. The ESW of solid electrolytes was usually measured from the Li/SE/inert metal semi-blocking electrode. Because of the wide ESW, solid electrolytes hold great promise for high energy density batteries with high columbic efficiency and long cycle life. In this dissertation, we challenge the claimed ESW of solid electrolytes. The conventional method to measure ESW provides an overestimated value because the kinetics of the electrochemical decomposition reaction is limited in the semi-blocking electrode. A novel experimental method using Li/SE/SE+carbon cell is proposed to approach the intrinsic stability window of solid electrolytes. The ESWs of Li10GeP2S12 (LGPS) and Li7La3Zr2O12 (LLZO), the most promising SE for sulfide and oxide electrolytes respectively, are examined using the novel experimental method. The results suggest that both SEs have much narrower electrochemical stability window than what was previously claimed. The cathodic and anodic decomposition products for both electrolytes are also characterized. The measured stability window and the decomposition products agree well with the calculated results from first principles. The reversible decompositions of LGPS at both high and low voltages enable the realization of a battery made from a single material. The electrochemical decompositions of the SEs in ASSLIBs can lead to large interfacial resistances between electrode and electrolyte. The interfacial resistances arising from the decomposition of SEs have been ignored in previous research efforts because the batteries are cycled within the “claimed” stable window of SEs. Suppressing the (electro)chemical reactions between LiCoO2 cathode and LLZO electrolyte by engineering their interphase enables a high performance all-ceramic lithium battery. By taking advantage of the electrochemical decomposition of SEs, an effective approach to suppress Li dendrite formation in sulfide electrolyte is also demonstrated.Item THE UPGRADING OF METHANE TO AROMATICS OVER TRANSITION METAL LOADED HIERARCHICAL ZEOLITES(2017) WU, YIQING; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the boom of shale gas production, the conversion of methane to higher hydrocarbons (MTH) promises a great future as the substituent for hydrocarbon production from crude oil based processes. Among various MTH processes, direct methane aromatization (DMA) is promising since it can achieve one-step methane valorization to aromatics. The molybdenum/zeolite (Mo/MFI or Mo/MWW) has been the most active catalyst for the DMA reaction, which, however, is impeded from industrial practice due to the rapid deactivation by coke deposition. To address this challenge, in this work, transition metal loaded hierarchical 2 dimensional (2D) lamellar MFI and MWW zeolites have been studied as catalysts for the DMA reaction. The effects of micro- and mesoporosity, external and internal Brønsted acid sites, as well as particle size of 2D lamellar zeolites on the DMA reaction have been investigated. Firstly, the spatial distribution of Brønsted acid sites in 2D lamellar MFI and MWW zeolites has been quantified by a combination of organic base titration and methanol dehydration reaction. The unit-cell thick 2D zeolites after Mo loading showed mitigation on deactivation, increase in activity, and comparable aromatics selectivity to the Mo loaded 3D zeolite analogues. A detailed analysis of the DMA reaction over Mo/hierarchical MFI zeolites with variable micro- and mesoporosity (equivalent to variation in particle sizes) showed a balance between dual porosity was essential to modulate the distribution of active sites (Mo and Brønsted acid sites) in the catalysts as well as the consequent reaction and transport events to optimize performance in the DMA reaction. External Brønsted acid sites have been proposed to be the cause of coke deposition on Mo/zeolite catalysts. Deactivation of the external acid sites have been practiced to improve the catalyst performances in the DMA reaction in this work. Atomic layer deposition (ALD) of silica species was conducted on the external surface of 2D lamellar MFI and MWW zeolites to deactivate the external acid sites in Mo/2D lamellar zeolites for the DMA reaction. Another strategy to deactivate external acid sites in Mo/zeolite catalysts was the overgrowth of 2D lamellar silicalite-1 on the microporous zeolites. The as-prepared catalysts showed higher methane conversion and aromatics formation as well as higher selectivity to naphthalene and coke in comparison with Mo loaded microporous analogues.Item Beyond Li ion: Rechargeable Metal Batteries based on Multivalent Chemistry(2017) Gao, Tao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of advanced battery technology with lower cost and higher energy density is important since various mobile applications are becoming indispensable in our daily life. While Li chemistry has approached its theoretical limit after several decades’ increment improvement, the potential of multivalent chemistry (Mg, Al, etc.) remains unexplored. Compared to Li ion chemistry, multivalent chemistry provides many intriguing benefits in terms of lowering cost and increasing energy density. First of all, minerals containing multivalent element such as Mg, Al, and etc. are much more abundant and cheaper than Li. Second, multivalent metals (Mg, Al etc.) can be directly used as anode materials, ensuring much higher anode capacity than graphite currently used in Li-ion battery. Third, the divalent or trivalent nature of the electroactive cation (Mg2+and Al3+) also promise high capacity for intercalation cathodes because the capacity of these materials are limited by their available ion occupancy sites in the crystal structure instead of its capability to accept electrons. In this dissertation, I detailed our efforts in examining some redox chemistries and materials for the use of rechargeable batteries based on multivalent metal anodes. They include intercalation cathode (TiS2) and conversion cathode (sulfur, iodine). We studied their electrochemical redox behavior in the corresponding chemistry, the thermodynamics, kinetics as well as the reaction reversibility. The reaction mechanism is also investigated with various macroscopic and spectroscopic techniques.Item Organic Anodes and Sulfur/Selenium Cathodes for Advanced Li and Na Batteries(2015) Luo, Chao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To address energy crisis and environmental pollution induced by fossil fuels, there is an urgent demand to develop sustainable, renewable, environmental benign, low cost and high capacity energy storage devices to power electric vehicles and enhance clean energy approaches such as solar energy, wind energy and hydroenergy. However, the commercial Li-ion batteries cannot satisfy the critical requirements for next generation rechargeable batteries. The commercial electrode materials (graphite anode and LiCoO2 cathode) are unsustainable, unrenewable and environmental harmful. Organic materials derived from biomasses are promising candidates for next generation rechargeable battery anodes due to their sustainability, renewability, environmental benignity and low cost. Driven by the high potential of organic materials for next generation batteries, I initiated a new research direction on exploring advanced organic compounds for Li-ion and Na-ion battery anodes. In my work, I employed croconic acid disodium salt and 2,5-Dihydroxy-1,4-benzoquinone disodium salt as models to investigate the effects of size and carbon coating on electrochemical performance for Li-ion and Na-ion batteries. The results demonstrate that the minimization of organic particle size into nano-scale and wrapping organic materials with graphene oxide can remarkably enhance the rate capability and cycling stability of organic anodes in both Li-ion and Na-ion batteries. To match with organic anodes, high capacity sulfur and selenium cathodes were also investigated. However, sulfur and selenium cathodes suffer from low electrical conductivity and shuttle reaction, which result in capacity fading and poor lifetime. To circumvent the drawbacks of sulfur and selenium, carbon matrixes such as mesoporous carbon, carbonized polyacrylonitrile and carbonized perylene-3, 4, 9, 10-tetracarboxylic dianhydride are employed to encapsulate sulfur, selenium and selenium sulfide. The resulting composites exhibit exceptional electrochemical performance owing to the high conductivity of carbon and effective restriction of polysulfides and polyselenides in carbon matrix, which avoids shuttle reaction.Item MODIFICATION OF MIXED PROTON-ELECTRON CONDUCTORS FOR HYDROGEN TRANSPORT MEMBRANES AND INVESTIGATION OF AMMONIA ION TRANSFER MEMBRANES(2015) Liang, Xuan; Wachsman, Eric; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)SrCe0.9Eu0.1O3- δ has low electron conductivity that limiting the hydrogen permeation. Effects of different dopants in SrCeO3 were studied in order to find new materials that have higher electron conductivity. Total conductivities of these materials and transference number of each species were used for calculating the electron and proton conductivities in the mixed ionic electronic conductors. SrCe0.9Pr0.1O3- δ was claimed to have higher electron conductivity than SrCe0.9Eu0.1O3- δ. The hydrogen permeability of SrCe1-xPrxO3- δ was studied as a function of temperature, hydrogen partial pressure gradient and water vapor pressure gradient. Modified Nafion® membranes can be used for electrochemical ammonia compression.Item Assembly and Combustion Properties of Energetic Mesoparticles(2015) Wei, Boran; Zachariah, Micheal R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energetic materials are materials which can release large amounts of energy in a short time interval. When the size of energetic materials is reduced from micro into nanoscale, the reactivity of energetic materials increases dramatically due to increase in intimate contact and faster mass and heat transfer. Finding an efficient way to synthesize energetic nanocomposites has become an import research topic. Here I demonstrate the use of electrospray methods to generate mesostructured microparticles containing nanomaterials and a gas generator. The system was designed for characterization of the size distribution as well as combustion properties. In this thesis, size distribution of the Al/NC mesoparticles is tuned from 0.7-2.0 µm, and the ignition delay is shown significantly decrease (15 ms to 3 ms) compared to nano-size Al. The burn time is also decreased significantly (4036 µs to 366 µs) by using electrospray assembly. This demonstrated that assembly of nanocomponents can significantly impact combustion performance.Item SOFT HYDROGEL BATTERIES: THE DANIELL CELL CONCEPTUALIZED IN HYBRID HYDROGELS(2015) Goyal, Ankit; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energy storage devices such as batteries are important elements in many electronic devices. Currently, researchers are seeking to create new electronic devices that are "soft", i.e., bendable and stretchable. However, the batteries that power such devices are still mostly hard structures. In the current thesis, we have attempted to develop a "soft" battery out of hydrogels. Specifically, we have made a soft version of the Daniell Cell, which is a classic electrochemical cell. Our design involves a hybrid gel composed of three distinct layers. The top and bottom layers are gels swollen with a zinc salt and a copper salt, respectively, while the middle layer is akin to a "salt bridge" between the two. The hybrid gel is made by a polymerization technique developed in our laboratory and it retains good mechanical integrity (i.e., the individual layers do not delaminate). Zinc and copper foils are then attached to the hydrogel, thus creating an overall battery, and its discharge performance is reported. One unique aspect of these gel batteries is that they can be dehydrated and stored in a dry form, whereupon they are no longer batteries. In this inactive state, the materials are safe and light to transport. Upon rehydration, the gels revert to being functional batteries. This concept could be useful for military or other applications where an emergency energy storage is needed.Item TELLURIUM/POROUS CARBON COMPOSITE CATHODE FOR LI-ION BATTERIES AND CARBON NANOFIBERS ANODE FOR NA/K-ION BATTERIES(2014) LIU, YING; Wang, Chunsheng; Bigio, David; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon materials are often used to enhance the electronic conductivity in anodes or cathodes of Li-ion batteries (LIBs), as well as to support other active materials in high-capacity nanocomposite electrodes. A novel lithium-tellurium battery was established here using tellurium/porous carbon composite (Te/C), which was synthesized by a vacuum-liquid-infusion method. Owing to the physical confinement of Te by porous carbon matrix, the Te/C electrode is capable to deliver a high reversible volumetric capacity of 1400 mAh/cm3 for up to 1000 cycles and exhibits a good rate capability. In addition, in situ study of the electrochemically-driven sodiation and potassiation of individual bilayer carbon nanofibers (CNFs) by transmission electron microscopy (TEM) was also conducted to investigate the application of carbon based materials in sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs), which indicates that disordered carbon possesses great potential for sodium and potassium storage.Item AEROSOL SYNTHESIS OF CATHODE MATERIALS FOR NA-ION AND LI-ION BATTERIES(2014) Langrock, Alex; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energy production and storage are important issues that play a key role in our daily lives. There is a need for high energy and high power systems for portable electronic devices and zero-emission vehicles. Lithium-ion batteries are crucial in addressing these needs. However, for the smart electric grid and renewable energy storage where cost is critical but weight and footprint requirement is less important, the sodium-ion battery is the most suitable power sources. To achieve both high power density and high energy density, nanostructured sphere particles with controlled porosity and high tapping density are desired for both Li-ion and Na-ion batteries. The versatile and facile ultrasonic spray pyrolysis method allows for the synthesis of a variety of electrode materials with sphere morphology. Work has been done to develop electrode materials through an aerosol method that can be readily applied to industry. Two classes of high energy cathodes suitable for lithium-ion batteries were studied. These include the 5V spinels and lithium-rich materials. The 5V spinels are a promising class of electrodes for secondary lithium batteries. This class of material has the highest intrinsic rate capability of the intercalation cathodes with high safety, low toxicity, and low cost making it ideal for high-power applications such as electric vehicles, while the lithium-rich compounds exhibit high capacity and reasonable cycle stability. Two classes of stable cathodes suitable for sodium-ion batteries were studied. The first was carbon coated porous hollow Na2FePO4F spheres with 500 nm diameter and 80 nm wall thickness synthesized by a one-step template-free ultrasonic spray pyrolysis process using sucrose as the carbon source. Nano-sized porous hollow Na2FePO4F spheres allow electrolyte to penetrate into the hollow structure, and thus the electrochemical reaction can take place on both the outside and inside surface and in the pores. Also, the carbon coating on Na2FePO4F hollow spheres enhances the electronic conductivity and charge transfer reaction kinetics. The exceptional performance of hollow Na2FePO4F spheres combined with mature aerosol spray synthesis technology make these carbon coated porous hollow Na2FePO4F spheres very promising as cathode materials for practical applications in Na-ion batteries. Finally, P2-type earth abundant layered oxides with high energy density and long cycling stability were also developed and studied. These layered materials were investigated due to their high theoretical capacity. A novel ultrasonic spray pyrolysis system has been developed to effectively coat any cathode, including layered oxides, with a thin layer of carbon to improve the kinetics and increase the electronic conductivity. The residence time in air is sufficiently short to allow the decomposition of the carbon source (sucrose) without further reduction of the cathode material. A vertical configuration allows the solid particles to reach the filter for collection with high efficiency. As a test sample, lithium-rich cathodes have been successfully carbon coated and compared with the bare material.